[ECOS] processes vs threads (MMU protection)

[Armando Visconti]

Thomas,

Thanks for information ....
We are evaluating the possibility of having such a
feature for our ARM based products. Even if we have
other higher priority stuff to do, we may evaluate to
start such activity on late september.
But I don't want to break from official eCos source code,
so I really hope your kernel changes will be soon included
in the repository ... As I told you, I think that all depends on
how many people are interested on MMU protection ...

Armando.


Thomas.Binder@frequentis.com wrote:

> Armando Visconti wrote:
> >
> > Thomas.Binder@frequentis.com wrote:
> >
> > > Hmm! I don't know the approach from 3GLabs, however, our process environment
> > > (i.e. the classes that implement processes + the interface the user sees) is
> > > *completely* architecture independent. All you need is a gcc2 or gcc3
> > > compiler. The HAL needed to be changed to support the page table load
> > > operation, that certainly *is* hardware dependent, but I guess that's what the
> > > HAL is for. What needs further discussion is whether it is better to create a
> > > new PPC HAL with MMU support, or to use compile time switches in the existing
> > > one.
> >
> > This looks fantastic to me. We have different products with different level
> > of complexity. What I would like to do is being able to decide through
> > configuration
> > (and this is the key factor of eCos, right?) whether I want to include the MMU
> > support or not!
>
> Yes, absolutely. The process environment (and paging mode) is totally configurable. We also have boards where we currently don't use memory protection at all.
>
> The memory protection comes in two stages, where the second (the process environment) depends on the first (the paging mode) to be turned on.
>
> > > [...]
> > > stack). Besides, our approach has been suggested in literature and was already
> > > successfully implemented (I think there's a citation of Millers paper in my
> > > original post).
> > >
> >
> > Where can I find some of the 'literature' you are reffering to?
> > This is just my curiosity ...
>
> You will find the citation plus some additional details in the announcement from April this year.
>
>         http://sources.redhat.com/ml/ecos-discuss/2003-04/msg00311.html
>
> > Is the documentation of how to port the HAL for supporting MMU already
> > available? Yes, I know ... we can't do anything without the kernel support,
> > but I'm curios to see what must be done to have such a support ...
>
> No, we don't have a HOWTO that describes the necessary tasks. However, most of the functions you will have to implement are map/or unmap functions. You will find those in a file called hal_process_misc.c.
>
> If you are really going to implement the MMU for another HAL I certainly can give you more detailed hints.
>
> best regards,
> Tom
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